Thermionic cathode space current tube



Jan. 12, 1937. w. J. HITCHCOCK THEBMIONIC CATHODE SPACE CURRENT TUBEFiled Oct. 12, 1932 2 Sheets-Sheet l INVENTOR 9. "Mud:

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Jan. 12, 1937 J HlTCHCOcK 2,067,607

THERMIONIC CATHQDE SPACE CURRENT TUBE Filed Oct. 12, 1952 2 Sheets-Sheet2 @Zz'gafii 5.: 65'

Wil 21 1 4! Patented Jan. 12, 1937 CURRENT TUBE V William I. Hitchcock,Scotia, N. Y.

Application October 12, 1932, Serial No. 637,433

7 Claims. (01. 250-275) The present invention relates to hot cathodespace current devices such as thermionic vacuum tubes and the like.

The principle underlying the present invention resides in the design orarrangement of the electrodes with a view to improving the, thermaleiiiciency and certain other operating characteristics, as will appearfrom a description of one or two practical embodiments of the invention.1

In all devices in which space currents are maintained by the emission ofelectrons from a hot cathode heat and light energy are liberated at theanode through condensation of '15 electrons and by the impact ofelectrons. An

' 25 tant results of this being to make more practical the use ofcaesiated surfaces or alkaline earth surfaces as hot cathodes. These andother important results, which will be apparent, are obtained byenclosing the anode entirely or 30 substantially entirely by the cathodeso that heat and light liberated at the anode by the condensation andimpact of electrons may substantially all be supplied by radiation tothe surrounding cathode for the maintenance of the proper electronemission temperature, while at the same time enabling the cathode to beconstructed of such large area as to greatly improve the emission andminimize sputtering. Such a 40 cathode may have a polished outer surfaceto reduce radiation, and may furthermore be surrounded by suitableradiation shielding to minimize the loss of heat and light energythrough radiation.

45 The principles of the invention are applicable to many differenttypes of hot cathode space current devices, whether high or low vacuumor 9 gas filled, but will be made sufiiciently clear by reference toexamples in the form of a ther- 50 mionic rectifier and a screen gridvacuum tube as used in present-day radio circuits.

In the accompanying drawings Figure 1 is a side'elevation of a full waverectifier tube constructed in accordance with my 55 present invention.

Figure 2 is an enlarged central vertical section thereof.

Figure 3 is a transverse section thereof on the line 3-3 of Figure 2.

Figure 4 is'a circuit diagram showing the electrical connections of thefull wave rectifier tube in a standard power supply for radio receivers.

Figure 5 is a side ,elevation of a screen grid vacuum tube constructedin accordance with my present invention.

Figure 6 is an enlarged central vertical section thereof.

Figure 7 is a circuit diagram showing the connection of the screen gridtube in a typical high frequency radio receiver circuit.

Referring to Figures 1 to 4 inclusive, the hot cathode may comprise asheet metal cylinder III of nickel, tungsten or the like, having endcaps or heads ll, [2 at top and bottom, mounted within a radiationscreen I3 which has the cover M at the top and the closure at thebottom. The cathode I!) may have a bright outer surface to minimizeradiation, and its interior surface may be oxide-coated or caesiated, orotherwise treated for the eflicient emission of electrons. It iselectrically and mechanically connected with the radiation screen l3 bythe metallic spacing ring I6 at the top. The screen I3 is supported atthe bottom by a pair of leadin insulators i1 and I8, of thoria or thelike, which are mounted in the glass neck I!) of the bulb 20. Suchlead-in insulator tubes l1, l8 pass through suitable perforations in thebottom closure l5 of the screen l3, and are secured thereto by a pair ofclamping straps 2|, as clearly shown in Figures 2 and 3. A conductor 22,leading from one of the terminals of the rectifier tube and passingthrough the sealing neck IQ of the bulb, may be connected with thescreen l3 and through it by way of the spacing ring l6, to the cathodeI0.

When employing two anodes the space within the cathode i0 is dividedinto upper and lower chambers by the transverse partition 23, which maybe of the same material as the cathode III. A cylindrical anode 24 oftubular metal construction, provided with an upper transverse wall 25,is mounted in the cathode chamber above the partition 23 upon asupporting conductor 26, which is surrounded by a collar 21 ofinsulation and passes through an insulating bushing 28 which is insertedthrough registering perforations in the screen 13 and cathode I 0. Thisconductor 26 passes from the insulating bushing HEB-downwardly throughthe neck IQ of the bulb to one of the anode terminals of the tube. Asimilar tubular anode 29 is moimted on a supporting conductor 30 whichpasses through the insulator tube l8 above-mentioned, the conductor 30being connected with the second anode terminal of the rectifier tube. Aheating resistance 3|, connected at the top to the conductor 30, iscoiled around the insulator tube I8 and brought out by conductor 32through insulator tube I! to be connected with another terminal of therectifier tube. This heater coil 3| may be employed only in starting, orcontinuously, for the purpose of indirectly heating the cathode H! byradiation from the anode 29, but will ordinarily not be required afterthe cathode has been brought up to the emission temperature.

The circuit diagram in Figure-4 shows the heating coil 3| in the form ofa filament electrically connected with the anode 29, which latter iswithin the tubular cathode Ill. The second anode 24 is also shown .asbeing located within the cylindrical cathode 10. The power supplyprimary coil 33 feeds a secondary transformer coil comprising theheating winding 34 and the plate supply winding 35, which latter isconnected at one end by conductor 26 with the anode 24, and at the otherend by way of the conductor 32, previously mentioned, to the anode 29.The cathode has the lead-in conductor 22 connected through choke 36,voltage divider 31, conductor 38, 39 and 40 to the midpoint on thewinding 35 of the transformer secondary. The filter circuits arestandard practice and require no further description.

The operation of the device will be apparent to those skilled in theart. Power delivered from the primary 33 and secondary 34 will heat theanode 29 which radiates heat to cathode Ill. The conduction of heatthrough the metal of the cathode will bring all portions of it up toemitting temperature, so that the thermionic or electron current willflow between cathode and the respective anodes 24, 29 as theyalternately become positive with respect to the cathode. The impact andcondensation of electrons on the anode surface develop heat and lightenergy which is radiated to the cathode. Since the anode in such case isnecessarily at all times hotter than the cathode, it must of course beunderstood that the cathode employed is one which 1 emits electrons at atemperature well below that at which any substantial emission wouldoccur from the anodes.

The example of a screen grid radio tube, illustrated in Figures 5, 6 and'7, follows in principle the construction already described inconnection with the rectifier tube. A glass or pyrex bulb 56 has leadingfrom its neck a supporting conductor 52, which is connected at thebottom with a lead-in wire 53 extending from one of the tube prongs tothe radiation screen 54, which has mounted in its top an annularmetallic sheet 55 with inner and outer peripheral flanges 56, 51. In theinner peripheral flange 56 is inserted an insulator 58, on which ismounted the flanged cap 59 of the cathode 60. The cathode 60 is oftubular construction, with an out-turned peripheral flange 6| restingupon an in-tumed peripheral flange 62 of the screen 54. By thisconstruction the cathode is electrically connected with the screen 54and through the latter to the supporting wire 52 and the lead-in 53. Asecond supporting wire 63 is provided to steady the mounting. The anodeor plate electrode in this example is in the form of an axial rod 64which depends from the insulator 56 at the top,

where the plate lead 65 is connected. Surroundtom of the cathode. Thescreen grid in thisinstance serves as the preliminary heater, and forthis purpose it is connected at one end with the lead-in wire 10, whichpasses through the neck 5| of the bulb. The two sections of the helixmay be, for example, electrically connected at the top by the metallicdisk 61, above-mentioned. The other end of the screen grid is connectedelectrically with the metallic disk 68 at the bottom of the cathode,which latter has electrically connected with it the lead wire II. Theleads 10, ll thus constitute the terminals of the preliminary heatercircuit, and at the same time the connection through which the operatingpotential is applied to the screen grid in the receiver circuit. Theyare accordingly connected to the proper prongs in the base of the -tube.Surrounding the. screen grid 66 is the normal or control grid which isin the form of a helix 12, mounted between conductive supporting wires13, 14 which pass through the insulation plug 69 at the bottom of thecathode. The supporting wire 14 is mounted in the neck 5| of the bulb.The supporting wire .13 has electrically connected with it the lead 15,which passes through the neck 5'! and is connected with the proper prongof the tube base.

The plate lead 65, above-mentioned, is shown in Figure 5 as beingconnected with the usual contact post 16 mounted in the top of the bulb.

By reference to Figure 7, the electrical connection of the various partsin the receiving circuit will be apparent. The terminals 10, H of thescreen grid are connected across a secondary winding 11 of a heatingtransformer, the primary 18 of which may be switched in at the time ofheating up the tube. The heating of the screen grid bringsthe cathode upto the proper emission temperature, which may thereafter be maintainedby the radiationof heat from the anode, as already explained. Thecathode 60 is repre-- sented diagrammatically in Figure 7 in the form ofthe usual filament, the screen grid being indicated at 66, the anode at64, and. the control grid at 12. A screen grid lead wire 19 leads from asuitable tap on thepower source 80 to a midpoint 8| on the secondarywinding 11. The anode lead 65 passes through plate inductance 66 to thehigh tension lead 82 of the power source, the cathode lead 53 connectsat a suitable voltage point with the power source 89, and the controlgrid lead 15 connects in this instance through a grid resistance 83 andconductor 84 with the negative side of the power source 80.

Insofar as the enclosure of the anode within the cathode is connected,the advantages already pointed out in connection with the rectifier tubepertain also to the screen grid tube. There are in addition importantadvantages present in the screen grid tube. The electrostatic capacitybetween the plate and the control grid of the tube is reduced by thesmall area of the plate or anode. The mutual conductance of the tube isconsiderably improved by the relatively large emitting surface of thecathode. Caesiated or other cathode surfaces which emit at relativelylow temperatures are advantageous in the oathode in the presentinstance, even though the 01' devices in which the operation dependsupon cathode" always remains negative with respect to the anode or plateelectrode. 7

The examples given are not to be taken as limitingthe scopeof theinvention to the em.- pioyment o! itsprinciples in these particulartypes. of space current devices, since the functions pertaining to the.inventionare applicable quite generally to many diderent specific formsthe application of heat to a cathode for the purpose of causing the.emission of electrons.

The anode and .cathode may each be in the form of either. a singleelement or a plurality of elements; that is to. say, there may be onesingle anode or two or more anodes, and one single cathode or two ormore cathodes. In any case, however, the entire electron current fromthe cathode system isdirected inwardly to the anode system, in thenormal operation of the tube, and the. heat developed at the anode islargely conserved and delivered by radiation and conduction outwardlytothe surrounding cathode system.

I claim: I

l. A rectifier tube comprising a cathode having a thermionic surfaceextending around its own emission space and provided-with anintermediate partition extending transversely across the enclosedemission space, and an anode in each of the emission spaces separated bysaid partition.

2. A thermionic tube comprising a substantially closed cathode having aninner surface electron emitting when heated, and an anode and a heaterboth disposed within said cathode, whereby said cathode may be heated toelectron emitting temperature by radiation from within said cathode.

3. A thermionic tube comprising a substantially closed cathode having aninner surface electron emitting when heated, a plurality of spacedanodes disposed within said cathode, an intermediate partition extendingtransversely across said cathode and between said anodes to separate thelatter, and a heater enclosed with an anode within said cathode, wherebysaid cathode may be heated to electron emitting. temperature byradiation from within said cathode,

initially from said heater and subsequently by heat radiated from saidanodes during the operation of the tube.

- 4. A thermionic tube comprising a tubular sheet metal thermioniccathode closed at its ends and having an inner surface electron emittingwhen heated, an anode and a heater both disposed within said cathode,and a radiation screen completely enclosing said cathode, whereby saidcathode may be heated to electron emitting temperature by radiation andconduction. from within said'cathode, initially from said heater andsubsequently by heat radiated and conducted from said anode during theoperation of the tube.

5. A thermionic tube comprising a tubular sheet metal thermioniocathodeclosed at its ends and having an inner surface electron emitting whenheated, an anode and a heater both disposed within said cathode wherebysaid cathode may be heated to electron emitting temperature by radiationand conduction from within said cathode initially fromv said heater andsubsequently by heat radiated and conducted from said anode during thenormal operation of the the tube, and a'grid electrode disposed betweenI said cathode and anode and enclosed within said cathode.

7. A screen grid thermionic tube comprising a tubular thermionic cathodeclosed at its ends'and having an inner surface electron emitting whenheated, a. control grid, a filamentary screen grid and an anode, alldisposed within said cathode, whereby said cathode may be heatedentirely from within to electron emitting temperature by radiation 'fromsaid screen grid serving as a filamentary heating element when the tubeis started, and subsequently by heat radiated from said anode and screengrid during the normal operation of the tube.

WILLIAM J. HITCHCOCK.

